As more people populate urban environments, there is an increasing need to provide a clean air environment at home and in the work place. In urban areas, where pollution levels sometimes exceed maximum values set by the EPA, the need for a clean air environment becomes even more apparent. In view of the hazards these polluted environments pose, the public has demanded a means for removing pollutants from the environment to provide a healthy environment for both living and working. Furthermore, many particles in the air can act as irritants and/or increase or aggravate a person's allergies. Airborne pollutants can also contribute to respiratory infections and/or illnesses which can be discomforting and/or hazardous to individuals with respiratory problems. Particles in the air can also create problems such as burning eyes, nose and/or throat irritation; cause or contribute to headaches and dizziness; and/or cause and/or contribute to coughing and sneezing. Furthermore, these particles can include various types of spores, dust mites, micro-organisms (e.g., bacteria, viruses, etc), allergens, and/or other types of harmful particles which may cause illness and/or infection to a person; and/or induce and/or aggravate respiratory ailments (asthma, RSV, lung cancer, etc.).
In an effort to reduce the number of particles in the air and/or other environments, many homes, offices, and buildings have incorporated a central filtering system to remove particles entrained in the air. Unfortunately, these systems are very expensive and/or do not remove many of the small particles which can be the most hazardous and/or irritable to persons (e.g., spores, allergens (e.g., pollen, smoke, etc.), micro-organisms (e.g. bacteria, viruses, etc.), dust mites, asbestos, metals, harmful and/or irritating chemicals, etc.). Typically, these filtering systems only remove about 300,000 particles out of about 20 million particles which flow into the filter medium. The small particles, which make up a majority of the particles in the air, freely pass through these conventional filter systems and are recirculated through the home and/or office.
In an effort to remove particles from a home and/or office environment, and reduce the amount of particles recirculated during the vacuuming of the home and/or office, two design strategies have been developed by Assignee, one relating to the design of the vacuum cleaner and the second relating to the design of the filters. Assignee has found that canister type vacuum cleaners provide superior cleaning efficiencies as compared with upright vacuum cleaners. One particular canister type vacuum cleaner is illustrated in U.S. Pat. No. 5,248,323, which is incorporated herein by reference. The canister type vacuum cleaner includes a reduced or low velocity chamber with a high velocity air inlet. Air is drawn into the low velocity chamber by an electric motor which drives a rotary fan. The rotary fan creates a vacuum in the low velocity chamber to draw air laden with particulate material through the chamber and to blow the filtered air through an outlet in the motor housing as exhausted cleaned air. Canister type vacuum cleaners normally include a cylindrical or a conical cellulose filter extending downwardly into the canister or low velocity chamber. The filter is typically formed of a porous mat to remove dirt and debris carried by the air drawing into the low velocity chamber. The high velocity air drawn into the chamber has entrained large solid particles. The large particles which are brought into the low velocity chamber are swirled or vortexed in a centrifuge configuration with convolutions so that the large particles are extracted by the vortex or cyclonic action of the air in the canister. Thereafter, the air is pulled through the filter toward an upper motor that drives a fan which creates a vacuum in the canister or low velocity chamber. The fan then expels the filtered air outwardly through an exhaust passage, or passages, above the canister. A filter, such as a thin filter disc, is typically provided between the conical filter and the fan to at least partially prevent large particulate material that is inadvertently passed through the cylindrical or conical filter from contacting the fan. The '323 patent discloses the use of an activated charcoal-containing filter to efficiently remove gaseous impurities in the air, such as, but not limited to, paint fumes and other odor creating gases.
The canister type vacuum cleaner, as so far described, though exhibiting improved cleaning efficiencies as compared with upright vacuum cleaners, only removed relatively large particles entrained in the air. Many of the air particles of a size less than 10 microns passed freely through the filter medium and were recirculated in the room. These small particles can act as irritants to an individual, and the recirculation of such particles can increase such irritation to an individual. High density filters can be used to filter out these very small particles in the air; however, high density filters cause large pressure drops through the filter and thus cannot be cost effectively used in standard vacuum cleaners.
The filter system disclosed in U.S. Pat. Nos. 5,593,479 and 5,651,811 addressed the problem of filtering small particles by disclosing a multi-layer filter which included at least one layer of electrically charged fiber material encapsulated between at least two layers of support material. The multi-layer filter effectively removed small particles from the air which penetrated the cellulose fiber layer. The multi-layer filter was a specialized filter developed to remove many of the small particles in the air. Such filters are known as High Efficiency Particle Air Filters, or HEPA filters, which, by government standards, are filters with a minimum efficiency of 99.97%. The industry defines HEPA filters as those which are efficient in removing 99.97% of the airborne particles having the size of 0.3 micron or larger. HEPA filters are commonly used in ultra clean environments such as in a laboratory, in electronic and biologically clean rooms, in hospitals, and the like. HEPA filters have recently been incorporated in air filters for business and/or individual use. The '479 and '811 patents disclosed that an activated charcoal filter could also be used to remove odors from the air.
The multiple filter system disclosed in the '479 and '811 patents was further improved by the filter system disclosed in U.S. Pat. No. 6,090,184. The filter system disclosed in the '184 patent combined an electrically charged fiber material with an activated charcoal filter to simplify the use of the filters in the vacuum cleaner. The combined filter reduced the number of filters to only the standard cellulose filter and the combined gas and small particle filter. The combined filter was designed to exhibit increased filter efficiency without added pressure drop. The efficiencies of standard HEPA filters are all based upon 0.3 micron size particles. Historically, it was believed that particles about 0.3 micron in size were the most difficult to remove from the air. However, particle filtration testing revealed that particles the size of about 0.1 micron are the most difficult to remove from the air. Standard HEPA filters do not efficiently remove such small particles and allow such particles to freely pass through the filter medium. An analysis of these small particles has shown that the particles do not naturally fall out of the air, but instead remain entrained in the air by constantly bouncing off other particles in the air (i.e. Browning effect). These small particles have also been found to deviate from the air flow, thus making such particles even more difficult to remove from the air. The filter disclosed in the '184 patent was designed to remove at least about 99.98% of the particles in the air that were about 0.1 micron or greater in size.
Although Assignee's vacuum cleaners and filter systems effectively and efficiently remove particles entrained in the air, there remained a demand for more efficient vacuum cleaners and more user friendly vacuum cleaners. This demand was effectively addressed in Assignee's U.S. patent application Ser. No. 09/809,841 filed Mar. 19, 2001. In the '841 patent application, a novel filter arrangement and vacuum cleaner design were disclosed which further improved the filtering efficiencies of the vacuum cleaner. In addition, the '841 patent application disclosed a unique vacuum cleaner design that facilitated in the ease of removal and/or replacement of the filter from the vacuum cleaner. Assignee's U.S. patent application Ser. No. 09/809,841 filed Mar. 19, 2001 is incorporated herein by reference.
Even with the significant improvements in filter design and vacuum cleaner design disclosed in Assignee's U.S. patent application Ser. No. 09/809,841 filed Mar. 19, 2001, there remains a need for a vacuum cleaner and vacuum cleaner filter that reduces the amount of particles expelled by the vacuum cleaner during use and which minimizes particle release from the vacuum cleaner filter when the vacuum cleaner filter is changed.